1. Field of the Invention
The present invention relates to a solid-liquid separating method for separating a slurry of a kind containing a mixture, of a liquid processing agent and solid particulate wastes, produced during a machining of metals, or of a kind produced during the wood working, into a solid component and a liquid component, and for solidifying the solid component to provide a compressed solidified product. The present invention also relates to an apparatus for performing the solid-liquid separation referred to above and to the compressed solidified product so obtained from the solid-liquid separation and the subsequent compressing of the solid component.
2. Description of the Prior Art
As is well known to those skilled in the art, during the practice of the various grinding processes such as, for example, honing, super processing and lapping, pulverized particles such as finely ground wastes are produced. Such pulverized particles are generally mixed with a processing liquid such as, for example, a liquid coolant to form a slurry or sludge, which is discharged out of the processing machine. The sludge so discharged is, in most cases, subjected to a solid-liquid separation with a filtering apparatus or a low pressure filter press so that the processing liquid separated from the pulverized particles can be recovered for reuse.
The solid-liquid separating method utilizing the filter or the low pressure filter press has been recognized to generate a processed sludge still having high content of liquid, resulting in such problems that not only can a sufficient amount of the processing liquid be recovered, but the sludge concentrated as a result of the solid-liquid separation cannot be recycled and is generally disposed of in land reclamation.
In order to alleviate the foregoing problems, the Japanese Laid-open Patent Publication No. 2001-300597, published Oct. 30, 2001, for example, discloses formation of a solid briquette of the ground sludge. Specifically, this published patent document discloses, as shown schematically in FIG. 11 of the accompanying drawings, supplying the concentrated sludge S′ into a cylindrical mold unit 51 and subsequently compressing the concentrated sludge S′ with a pressing rod 53 to provide a solid briquette. During the squeezing, one of opposite open ends of the mold 51 remote from the pressing rod 53 inserted into the mold unit 51 is closed by a gate 52, which is moved to an open position when the resultant solid briquette is to be discharged out of the mold unit 51. The sludge solidifying apparatus so discloses is currently utilized in practice.
The sludge solidifying apparatus including the cylindrical mold unit 51 and the pressing rod 53 such as disclosed in the above mentioned published patent document can work satisfactorily with the ground sludge made up of thread-like ground wastes that are relatively easy to entangle. However, such known sludge solidifying apparatus cannot work sufficiently with such sludge as sludge produced during honing, sludge produced during super-processing, sludge produced during lapping, and sludge produced during grinding of rolling elements such as, for example, bearing rollers and steel balls, because of the following reason.
Particulate wastes produced during those processes referred to above are finely divided and are so generally rounded as to render them to be difficult to entangle and, therefore, during the compression, some of them tend to flow out together with a liquid component through mechanical gaps δ1 and δ2 delimited between the mold unit 51 and the pressing rod 53 and between the mold unit 51 and the gate 52. In other words, while the standard ground wastes are so relatively large in particle size or represent such a thread-like shape as to render them to be easy to entangle, solidification of those standard ground wastes is easy to achieve without appreciably flowing out through the mechanical gaps δ1 and δ2 of the equipment, the sludge produced during the honing process contain the ground wastes so generally rounded as to render them to be difficult to entangle and, on the other hand, the sludge produced during the super processing and the lapping process are very finely divided. The sludge produced during the grinding of bearing rolling elements also contain finely divided ground wastes. For this reason, the conventional sludge solidifying apparatus referred to above cannot be satisfactorily used for solidifying or briquetting those sludge.
Not only does the flow of the ground wastes outwardly of the mold unit 51 through the mechanical gaps δ1 and δ2 discussed above render solidification or briquetting to be difficult to achieve, but the eventually recovered liquid component is still mixed with some of the ground wastes and, therefore, the processing liquid recovered cannot be reused satisfactorily, requiring the recovered processing liquid to be filtered even after the recovery thereof.
When it comes to the use of the ground sludge solidifying apparatus for solidifying or briquetting ground wastes such as produced during the honing process, an attempt is made to use a metallic filter held at a fixed position to thereby minimize or substantially avoid the undesirable flow of some of the ground waste outwardly through the mechanical gaps in the processing machine. However, it has been found that once the metallic filter is clogged, filtering no longer occurs and the metallic filter must be regularly replaced with a fresh one, requiring a complicated and time-consuming maintenance work.
As a method of treating the sludge other than that produced during the honing process, methods are known, in which a low pressure filter press and a sedimentation apparatus are used respectively. In the practice of the method using the low pressure filter press, a generally belt-shaped filter is used, through which the sludge is passed across the filter by the aid of a compressed air supplied into a sealed chamber.
However, both of those methods are incapable of reducing the liquid content of the sludge sufficiently. Specifically, the use of the sedimentation apparatus can barely reduce the liquid content down to about 50 to 80%. For these reasons, the efficiency of recovery of the processing liquid is so insufficient as to result in incapability of recycling the remaining concentrated sludge.